Reaction of ethylenically unsaturated compounds with hydrogen and carbon monoxide in the presence of a Group VIII metal compound or metal complex comprising such a Group VIII metal compound and a phosphorous compound, to produce the corresponding aldehydes is known as hydroformylation or oxo reaction. Production of aldedhydes by this reaction has been of high commercial value.
For the hydroformylation, rhodium complexes comprising rhodium and a phosphorous compound are used as catalysts commercially. It is known that, with hydroformylation, the reaction rate and the selectivity to a linear aldehyde (hereinafter referred to as “n-aldehyde”) or a branched aldehyde (hereinafter referred to as “iso-aldehyde”) depend significantly on the structure of the phosphorous compound constituting the catalyst used.
As the phosphorous compound, triphenylphospine, which is a monophosphine, is generally used commercially. In this case, the selectivity to n-aldehydes is low. In order to increase the selectivity to n-aldehydes, use of bisphosphines comprising two diphenylphosphines crosslinked together via a specific divalent organic group (hereinafter this group is referred to as “crosslinking group”) has been proposed.
For example, (1) it has been reported that with hydroformylation of propylene with use of 2,2′-bis(diphenylphosphinomethyl)biphenyl (hereinafter referred to as “BISBI”) the ratio of selectivities to n-aldehyde and iso-aldehyde (hereinafter referred to as “n/iso ratio”) is 25.1/1, which is markedly higher than 2.43/1, which is the case with triphenylphosphine which is a monophosphine (see U.S. Pat. No. 4,694,109); and (2) it is known that with hydroformylation of 1-octene with use of 9,9-dimethyl-4,6-bis(diphenylphosphino)xanthene (hereinafter referred to as “Xantphos”) the n/iso ratio is 53.5 [see Organometallics, 14, 6, 3081–3089(1995)].
According to the knowledge of the present inventor, although hydroformylation of 7-octen-1-al with the above BISBI or Xantphos can surely yield the corresponding n-aldehyde with higher selectivity than the reaction with triphenylphosphine, this reaction is not satisfactory due to low catalytic activity and, further, has problems that side reactions such as hydrogenation and isomerization occur.
With respect to the relationship between the structure of the bisphosphine used and the resulting n/iso ratio, it has been reported that, with a metal complex comprising a Group VIII metal compound and a bisphosphine, the closer to 120° the angle formed by phosphorus-rhodium-phosphorus is, the higher the n/iso ratio is [see Journal of the American Chemical Society, 114, 14, 5535–5543(1992) and Organometallics, 14, 6, 3081–3089(1995)]. However, the above literature report nothing about the relationship between the structure of the bisphosphine used and the selectivity to side reactions such as hydrogenation and isomerization.
Accordingly, an object of the present invention is to provide a bisphosphine constituting a hydroformylation catalyst that can, on hydroformylation of ethylenically unsaturated compounds, exert high catalytic activity and yield n-aldehydes with high selectivity while suppressing side reactions such as hydrogenation and isomerization.
Another object of the present invention is to provide a process for producing the above bisphosphine.
Still another object of the present invention is to provide a Group VIII metal complex that can act as a hydroformylation catalyst, said complex comprising the above bisphosphine and a Group VIII metal compound.
Yet another object of the present invention is to provide a process for producing aldehydes which comprises effecting hydroformylation of an ethylenically unsaturated compound with carbon monoxide and hydrogen with use of the above Group VIII metal complex.